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United States Patent |
6,124,210
|
Chino
,   et al.
|
September 26, 2000
|
Method of cleaning surface of substrate and method of manufacturing
semiconductor device
Abstract
The present invention relates to a method of cleaning a surface of a
substrate employed prior to film formation by using the CVD method which
uses a reaction gas containing an ozone containing gas which contains
ozone (O.sub.3) in oxygen (O.sub.2) and tetraethylorthosilicate (TEOS).
The substrate surface cleaning method comprises the steps of oxidizing
particles 13 by contacting a pre-process gas containing ozone 15 to a
surface 12 of a substrate 11 on which the particles 13 are present, and
removing the particles 13 by heating the substrate 11 to exceed a
decomposition point of oxide 13a of the particles 13.
Inventors:
|
Chino; Hiroshi (Tokyo, JP);
Suzuki; Setsu (Tokyo, JP);
Matsumoto; Hideya (Tokyo, JP);
Ohgawara; Shoji (Tokyo, JP)
|
Assignee:
|
Canon Sales Co., Inc. (JP);
Semiconductor Process Laboratory Co., Ltd. (JP)
|
Appl. No.:
|
317163 |
Filed:
|
May 24, 1999 |
Foreign Application Priority Data
| Mar 05, 1999[JP] | 11-058547 |
Current U.S. Class: |
438/706; 134/1.3; 257/E21.226; 257/E21.279; 438/477; 438/759; 438/770; 438/906; 438/974 |
Intern'l Class: |
H01L 021/322; H01L 021/302; H01L 021/31 |
Field of Search: |
438/477,690,706,765,759,758,800,770,906,974
134/1.3,1.2
|
References Cited
U.S. Patent Documents
5674357 | Oct., 1997 | Sun et al. | 156/659.
|
5749975 | May., 1998 | Li et al. | 134/1.
|
5782986 | Jul., 1998 | Butterbaugh et al. | 134/1.
|
5994240 | Nov., 1999 | Thakur | 438/758.
|
Foreign Patent Documents |
63-228620 | Sep., 1988 | JP.
| |
2-105416 | Apr., 1990 | JP.
| |
4-151831 | May., 1992 | JP.
| |
4-167431 | Jun., 1992 | JP.
| |
Primary Examiner: Bowers; Charles
Assistant Examiner: Lee; Hsien-Ming
Attorney, Agent or Firm: Lorusso & Loud
Claims
What is claimed is:
1. A method of cleaning a surface of a substrate on which particles are
present comprising the steps of:
oxidizing said particles by contacting a pre-process gas containing ozone
to said surface of the substrate; and
removing said particles by heating said substrate to exceed a decomposition
point of oxide of the particles.
2. The method of cleaning a surface of a substrate according to claim 1,
wherein charges on said surface of the substrate and the particles are
eliminated by contacting positive and negative ions to said surface of the
substrate before contacting said pre-process gas containing the ozone to
said surface of the substrate.
3. The method of cleaning a surface of a substrate according to claim 1,
wherein said particles are formed of alkaline metal salt.
4. The method of cleaning a surface of a substrate according to claim 3,
wherein said alkaline metal salt is composed of chloride of sodium or
chloride of potassium.
5. The method of cleaning a surface of a substrate according to claim 1,
wherein said particles are formed of alkaline earth metal salt.
6. The method of cleaning a surface of a substrate according to claim 5,
wherein said alkaline earth metal salt is composed of chloride of
magnesium or chloride of calcium.
7. The method of cleaning a surface of a substrate according to claim 1,
wherein the heating temperature of said substrate is set to more than
400.degree. C.
8. The method of cleaning a surface of a substrate according to claim 1,
wherein said pre-process gas containing the ozone is composed of a gas
mixture consisting of oxygen, ozone, and nitrogen.
9. The method of cleaning a surface of a substrate according to claim 1,
wherein an ozone concentration in said pre-process gas containing the
ozone is seat to 10 g/m.sup.3 (0.degree. C., 1 atmospheric pressure).
10. The method of cleaning a surface of a substrate according to claim 1,
wherein silicon is exposed on said surface of the substrate.
11. A method of manufacturing a semiconductor device comprising the steps
of:
contacting a pre-process gas containing ozone to a surface of a substrate
on which particles are present, thereby oxidizing said particles;
removing said particles by heating said substrate to exceed a decomposition
point of oxide of said particles; and
forming a silicon containing insulating film on said surface of the
substrate by a chemical vapor deposition using a film forming gas which
contains an ozone containing gas and a silicon containing gas.
12. A semiconductor device manufacturing method according to claim 11,
wherein said ozone containing gas is composed of a gas which contains
ozone in oxygen, and said silicon containing gas is composed of a gas
which contains at least one of tetraethylorthosilicate (TEOS),
trimethoxysilane (TMS), hexamethyldisilazane (HMDS), and
hexamethyldisiloxane (HMDSO).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of cleaning a substrate surface
employed prior to film formation by using the CVD (Chemical Vapor
Deposition) method which uses a reaction gas (hereinafter referred to as
an "O.sub.3 /TEOS reaction gas") containing an ozone containing gas which
contains ozone (O.sub.3) in oxygen (O.sub.2) and tetraethylorthosilicate
(TEOS), and a method of manufacturing a semiconductor device using the
above method.
2. Description of the Prior Art
In recent years, an insulating film can be formed by the CVD method using
the O.sub.3 /TEOS reaction gas (hereinafter referred to as an "O.sub.3
/TEOS-CVDSiO.sub.2 film"). The insulating film has fine quality and a
smaller etching rate, is not shrunk in the high temperature heating
process, has less moisture content, and has better flow performance as the
O.sub.3 concentration in O.sub.2 becomes higher. Where a silicon oxide
film which is formed by using the O.sub.3 /TEOS reaction gas containing
the high concentration O.sub.3 (called a "High O.sub.3 /TEOS reaction gas"
hereinafter) is called a High O.sub.3 /TEOS-CVDSiO.sub.2 film, and the
O.sub.3 /TEOS reaction gas containing the low concentration O.sub.3 is
called a "Low O.sub.3 /TEOS reaction gas.
Meanwhile, in the case that the High O.sub.3 /TEOS reaction gas is
employed, a degree of influence of the film formation upon surface
conditions of a film-forming surface (referred to as "surface dependency"
hereinafter) is increased. Where the film forming surface corresponds to a
surface of a substrate on which a film is planed to be formed. More
particularly, it has been known that, if as shown in FIG. 1A, a particular
extraneous substance, i.e., an particle 3 are present on a film-forming
surface 2 of a substrate 1, such particle 3 is melted down at the film
forming temperature to spread over (such area is indicated by a reference
3b), as shown in FIG. 1B, and then a deposition rate of the High O.sub.3
/TEOS-CVDSiO.sub.2 film 4 is extremely lowered in a range of several tens
.mu.m to several mm in diameter around the almost circular area, otherwise
the High O.sub.3 /TEOS-CVDSiO.sub.2 film 4 is not deposited at all in the
same range, as shown in FIG. 1C. This abnormal film forming phenomenon is
often called a circular defect, a spot fault, or the like.
In the prior art, prior to the formation of the O.sub.3 /TEOS-CVDSiO.sub.2
film, these extraneous particles are removed by cleaning the substrate by
the wet cleaning in the pure water. FIG. 2 is a flowchart showing the film
forming steps containing the pre-processing step according to the prior
art.
The circumstances in the clean room which is prepared to manufacture the
semiconductor device can be kept clean since floating particles are small
in number. Nevertheless, since the particles are produced due to the human
being such as the operator in many cases, such particles are often
detected from an inside of the clean room. Accordingly, even if the
substrate 1 is cleaned previously by the wet cleaning, there is a high
possibility that such particles are stuck to the substrate 1 again in the
clean room. As a result, it has been difficult to remove the foregoing
circular defect in the prior art.
SUMMARY OF THE INVENTION
The present invention has been made in view of above problem in the prior
art and it is an object of the present invention to provide a substrate
surface cleaning method which is employed prior to film formation and is
capable of suppressing generation of defective film formation in forming
an O.sub.3 /TEOS-CVDSiO.sub.2 film, particularly a high O.sub.3
/TEOS-CVDSiO.sub.2 film, and a semiconductor device manufacturing method
using this substrate surface cleaning method.
A gist of the present invention will be explained hereunder.
According to the examination made by the inventors of the present
invention, it has been found that the defective film formation generated
in forming the O.sub.3 /TEOS-CVDSiO.sub.2 film, especially the High
O.sub.3 /TEOS-CVDSiO.sub.2 film is caused by alkaline metal salt such as
sodium (Na) or potassium (K), and chlorine (Cl), contained in the
particles. In other words, it may be supposed that the existence of such
particles results in generating sodium chlorate or potassium chlorate
through the particles' being oxidized by the ozone in the film forming
gas, and then such sodium chlorate or potassium chlorate is melted at the
film forming temperature to then spread over the surface of the wafer, and
as a result the film forming defect is caused over the broad range.
By the way, it has been known that these sodium chlorate or potassium
chlorate are dissociated at the temperature of 482.degree. C. and
400.degree. C. respectively.
Based on the above-mentioned examination results, the inventors of the
present invention have concluded as follows. That is, in the event that
the particles formed of the alkaline metal salt are stuck onto the surface
of the wafer, before the film formation is commenced, the particles are
oxidized by supplying an oxidizing pre-process gas to the surface of the
wafer for a predetermined time and then the wafer temperature is kept at
the temperature in excess of the decomposition point of the oxidized
particle, whereby the particles can be effectively removed from the
surface of the wafer due to the dissociation and thus the surface of the
wafer can be cleaned. In this case, the ozone which has a very strong
oxidizing force is effective for the oxidizing gas contained in the
preprocess gas. Where the term "decomposition" employed in the above
signifies that the oxide of the particles is separated into constituent
elements, and is substantially equal to the term "dissociation".
Even if the film is formed on the surface of the substrate by the chemical
vapor deposition while using the film forming gas which contains the ozone
containing gas and the silicon containing gas, e.g., the film forming gas
like a gas mixture consisting of a gas containing ozone in the oxygen and
a gas containing TEOS, which is affected strongly by the surface
dependency in the film formation, the actual cleaning in this way deletes
such surface dependency in forming the film to thus lead to a normal
deposition of the silicon containing insulating film.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1C are sectional views showing semiconductor device
manufacturing steps indicating the problem in the prior art;
FIG. 2 is a flowchart showing an improved semiconductor device
manufacturing method in the prior art in the order of steps;
FIG. 3A is a flowchart showing a semiconductor device manufacturing method
using a film-forming surface cleaning method according to an embodiment of
the present invention;
FIG. 3B is a flowchart showing another semiconductor device manufacturing
method using another film-forming surface cleaning method according to the
embodiment of the present invention;
FIGS. 4A to 4C are sectional views showing a film-forming surface cleaning
method according to the embodiment of the present invention in the order
of steps; and
FIG. 5 is a top view showing a film forming equipment employed to carry out
the film-forming surface cleaning method according to the embodiment of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will be explained with reference to
the accompanying drawings hereinafter.
(Examination result to yield the present invention)
The inventors of the present invention have examined details of the
abnormal film forming area caused in forming the O.sub.3
/TEOS-CVDSiO.sub.2 film, particularly the High O.sub.3 /TEOS-CVDSiO.sub.2
film, and have accomplished the results described in the following.
That is to say, a minute particle 3a has been observed in the center area
of the abnormal film forming area shown in FIG. 1C. Constituent elements
of alkaline metal salt such as Na or K, and Cl have been detected by
analyzing components of this minute particle 3a.
According to the reproducing examination conducted to confirm the above
phenomenon, it has been found that, if the alkaline metal salt such as
KCl, KClO.sub.3, etc. is spread over a Si wafer, a large number of
circular defects are generated after the High O.sub.3 /TEOS-CVDSiO.sub.2
film is formed.
For example, NaCl and KCl as the representative alkaline metal salts have a
melting point of 801.degree. C. and 770.degree. C. respectively, and thus
they are chemically stable at the temperature of less than 660.degree. C.
as the film forming temperature. However, when the alkaline metal salts
are oxidized by a strong oxidizing force of O.sub.3 contained in the
O.sub.3 /TEOS reaction gas to be changed into alkaline metal chlorate
salts such as sodium chlorate (NaClO.sub.3), potassium chlorate
(KClO.sub.3), etc., their melting points are reduced to 261.degree. C. and
356.degree. C. respectively.
In this manner, if the alkaline metal chlorate salt is formed on the
surface of the wafer, it is melted on the surface of the wafer which is
kept at the film forming temperature higher than its melting temperature
and then spread over the surface of the wafer. Since the film formation of
the O.sub.3 /TEOS-CVDSiO.sub.2 film is extremely disturbed because of
surface contamination in the broad range, the film forming defect is
detected in a circular profile which is close to a substantially true
circle.
It has been known that above NaClO.sub.3 and KClO.sub.3 impede the film
formation since they melt down near the film forming temperature, while
above NaClO.sub.3 and KClO.sub.3 are dissociated at the temperature of
482.degree. C. and 400.degree. C. respectively. Thermal properties of KCl,
KClO.sub.3, and NaCl, NaClO.sub.3 are given in Table 1 as follows.
TABLE 1
______________________________________
Thermal stability of KCl, KClO.sub.3, and NaCl, NaClO.sub.3
Material
Melting Point
Boiling Point Dissociation Temp.
______________________________________
KCl 770.degree. C.
1500.degree. C. (sublimation)
KClO.sub.3
356.degree. C.
boiling point 400.degree. C.
decomposition
NaCl 801.degree. C.
1413.degree. C.
NaClO.sub.3
261.degree. C.
boiling point 482.degree. C.
decomposition
______________________________________
Based on the above-mentioned examination results, the following conclusion
can be supposed. That is, in the event that the particles formed of the
alkaline metal salt are stuck to the surface of the wafer (film-formed
substrate or substrate), before the film formation is commenced by
supplying the O.sub.3 /TEOS reaction gas to the surface of the wafer, the
particles are oxidized by supplying a pre-process gas containing O.sub.3,
e.g., an oxidizing gas mixture consisting of O.sub.2 containing O.sub.3
and N.sub.2, to the surface of the wafer for a predetermined time and then
the wafer temperature is kept at the temperature in excess of the
decomposition point of the oxidized particle, whereby the particles can be
removed effectively from the surface of the wafer due to the dissociation
and thus the surface of the wafer can be cleaned.
Even if the film is formed on the surface (film-forming surface) of the
substrate by the chemical vapor deposition while using the film forming
gas which is affected strongly by the surface dependency, the actual
cleaning in this way deletes such surface dependency in forming the film
to thus lead to a proper deposition of the silicon containing insulating
film. In this case, the film forming gas which contains the ozone
containing gas and the silicon containing gas, e.g., the film forming gas
like a gas mixture consisting of a gas containing ozone in the oxygen and
a gas containing TEOS, may be employed.
(Embodiment)
FIG. 3A is a flowchart showing a method of forming a film on a
semiconductor substrate including a film-forming surface cleaning method
according to an embodiment of the present invention. FIGS. 4A to 4C are
sectional views showing the film-forming surface cleaning method according
to the embodiment of the present invention in the order of steps. FIG. 5
is a top view showing a film forming equipment employed to carry out the
film-forming surface cleaning method according to the embodiment of the
present invention.
To begin with, the film forming equipment employed to carry out the
film-forming surface cleaning method according to the embodiment of the
present invention will be explained with reference to FIG. 5 hereunder.
As shown in FIG. 5, the film forming equipment comprises a transfer area
101 for a wafer (film-formed substrate or substrate), and a film forming
area 102 for the wafer.
Wafer cassettes 21a to 21c in which the wafers are stored before or after
film formation are provided to the transfer area 101. A transfer robot 22
is also provided to the transfer area 101. The transfer robot 22 transfers
the wafers 26 from the wafer cassettes 21a to 21c to the film forming area
102 before the film formation, and conversely transfers the wafers 26 from
the film forming area 102 to the wafer cassettes 21a to 21c after the film
formation. In addition, a discharge ionizer (not shown) is provided to the
transfer area 101. The electrostatically charged film-forming surface of
the wafer 26 can be discharged in the middle of transfer by generating
positive and negative ions from the discharge ionizer. In this case, if
the particles are stuck onto the film-forming surface, the electrostatic
charges on such particles can be eliminated simultaneously.
A circular-disk type wafer loading table 23 which is equipped with a
plurality of wafer loading portions 24a to 24f is provided to the film
forming area 102. The wafer loading table 23 is fixed. Also, a rotation
axis 25 of a transfer arm is provided to the center area of the wafer
loading table 23.
Six wafer loading portions 24a to 24f are provided on the circular-disk
type wafer loading table 23 along the circumference around the rotation
axis 25 of the transfer arm. The six wafer loading portions 24a to 24f are
provided respectively to carry out separate operations independently. The
wafer loading portion 24a located in the direct neighborhood of the
transfer robot 22 acts as a wafer transfer portion where the wafer is
temporarily held for transferring to next portion, and one film-forming
surface cleaning portion (A portion) 24b and four film forming portions (B
to E portions) 24c to 24f are provided clockwise in sequence along the
circumference.
The wafer transfer portion 24a receives the wafer 26 from the transfer
robot 22 prior to the film formation and then transfers the wafer 26 to
the transfer robot 22 after the film formation. In this case, a heating
means for heating the wafer preliminarily may be provided such that the
cleaning process before the film formation can be immediately carried out.
The film-forming surface cleaning portion (A portion) 24b executes the
cleaning process of the film-forming surface of the wafer by using the
oxygen gas containing ozone (O.sub.3). For this purpose, the film-forming
surface cleaning portion (A portion) 24b has a discharge port for the
oxygen gas containing the ozone (O.sub.3), and a wafer heating means for
heating the wafer during the cleaning process.
In the wafer loading portions (B to E portions) 24c to 24f, the film is
formed on the film-forming surface of the wafer by using the O.sub.3 /TEOS
reaction gas. For this purpose, a discharge port (or discharge ports) for
the reaction gas is (or are) provided to each of the wafer loading
portions 24c to 24f. In this case, as the discharge port(s) for the
reaction gas, either independent discharge port(s) which introduce the
O.sub.2 gas containing O.sub.3 and the TEOS gas separately into the wafer
loading portions 24c to 24f or one integrated discharge port which
discharges the O.sub.2 gas containing O.sub.3 and the TEOS gas as the gas
mixture may be employed. In addition, each of the wafer loading portions
24c to 24f has a heating means which causes thermal reaction of the
reaction gas.
The transfer arm (not shown) is then provided to the rotation axis 25
located at the center portion of the circular-disk type wafer loading
table 223. The transfer arm has a vacuum chuck or an electrostatic chuck,
and can be rotated clockwise, for example, around the rotation axis 25.
The transfer arm holds the wafer bag the vacuum chuck, or the like and
then transfers the wafer from one of the wafer loading portions 24c to 24f
to the other of the wafer loading portions 24c to 24f sequentially.
Next, a film-forming surface cleaning method using the above film-forming
equipment and a semiconductor device manufacturing method using this
cleaning method will be explained with reference to FIG. 3A, FIGS. 4A to
4C, and FIG. 5 hereunder.
First, the wafers 11 formed of silicon and contained in the wafer cassettes
21a to 21c in the transfer area 101 of the film-forming equipment in FIG.
5 are transferred to the film forming area 102 by using the transfer robot
22. In this case, assume that a film-forming surface 12 is composed of a
silicon surface and the particles 13 consisting of charged alkaline metal
salt are stuck onto the film-forming surface 12.
At this time, as shown in FIG. 4A, positive and negative ions 14 are
generated from the discharge ionizer. The film-forming surface 12 of the
wafer 11 and the particles 13, which are electrostatically charged, can be
neutralized by the positive and negative ions 14. Thus, electrostatic
sticking of additional particles onto the wafer 11 can be prevented, and
also the particles 12 which have already stuck onto the surface of the
wafer 11 can be easily removed from the surface of the wafer 11
physically.
The transfer robot 22 then loads the wafer 11 on the wafer transfer portion
24a on the wafer loading table 23 provided in the film forming area 102.
The wafer 11 loaded on the wafer :ransfer portion 24a is transferred to the
next film-forming surface cleaning portion (A portion) 24b by the transfer
arm. While, the transfer robot 22 installed in the transfer area 101 takes
out the next wafer 11 from the wafer cassettes 21a to 21c, then transfers
the wafer 11 to the film forming area 102 via the transfer area 101, and
then loads the wafer 11 onto the wafer transfer portion 24a.
The film-forming surface cleaning portion (A portion) 24b for the wafer 11
supplies the preprocess gas 15 containing O.sub.3, e.g., an oxidizing gas
mixture consisting of the O.sub.2 gas containing O.sub.3 and the N.sub.2
gas, to the film-forming surface 12 of the wafer 11 for the predetermined
period of time. Therefore, as shown in FIG. 4B, the particles 13 being
stuck onto the surface of the wafer 11 are oxidized. At the same time, the
wafer 11 is heated up to the decomposition point or more of the particle
oxide 13a, preferably about 400.degree. C. or more, and then kept at that
temperature. As a result, the particles 13 can be escaped effectively from
the surface of the wafer 11 due to the dissociation and thus the surface
of the wafer 11 can be cleaned. Conditions of the pre-process are given in
Table 2 (the item of the cleaning portion A). 0 g/Nm.sup.3 set forth in
the item of O.sub.3 concentration indicates that the pre-process is
applied to the case where an unprocessed sample is prepared. In this case,
in g/Nm.sup.3, `N` denotes abbreviation of `normal` which is the measuring
conditions of the temperature of 0.degree. C. and the atmospheric pressure
of 1, and denotes the density at the temperature of 0.degree. C. and the
atmospheric pressure of 1 in overall unit g/Nm.sup.3.
TABLE 2
______________________________________
Process Conditions
Cleaning portion
Film forming portions
Item A B, C, D, E
______________________________________
Wafer temperature
500.degree. C.
500.degree. C.
O.sub.2 flow rate
7.5 slm 7.5 slm
N.sub.2 flow rate
23.0 slm 23.0 slm
TEOS flow rate
0 slm 5.125 slm
O.sub.3 concentration
0 or 100 g/Nm.sup.3
140 g/Nm.sup.3
______________________________________
The wafer 11 whose film-forming surface 12 has been cleaned is then
transferred to the wafer loading portions 24c to 24f acting as the next
film forming portions (B to E portions) by the transfer robot, and also
the wafer 11 positioned on the wafer transfer portion 24a is transferred
to the film-forming surface cleaning portion (A portion) 24b. Also, the
new wafer 11 is transferred from one of the wafer cassettes 21a to 21c to
the wafer transfer portion 24a. The film-forming surface of the wafer 11,
when transferred to the film-forming surface cleaning portion (A portion)
24b, is cleaned there.
Four sheets of wafers 11 which are electrostatically discharged by
repeating the above steps are loaded on four film forming portions (B to E
portions) respectively.
The film forming gas like the gas mixture consisting of the gas containing
the ozone in the oxygen and the gas containing TEOS, which has the strong
surface dependency, is then discharged. A silicon containing insulating
film 16 is then formed on the film-forming surfaces of the wafers being
loaded on four film forming portions (B to E portions) by the chemical
vapor deposition. Film forming conditions employed in this case are given
in above Table 2 (the item of the film forming portions B, C, D, E).
Examination results concerning the situations of the circular defect
generated after the film formation are given in Table 3.
TABLE 3
______________________________________
Occurrence of Circular Defect
Process O.sub.3 concentration
Occurrence of Circular
Item time (sec)
(g/Nm.sup.3) Defect (l/wafer)
______________________________________
unprocessed
0 0 5.13
N.sub.2 process
30 0 2.75
60 0 2.75
90 0 2.25
O.sub.3 process
30 100 3.0
60 100 2.0
90 100 0.5
______________________________________
As the examination sample, while using an Si wafer having a diameter of 8
inch (200 mm), the substrate on which the film is formed after executing
the cleaning process under the conditions given in Table 2 (in the case of
the O.sub.3 concentration of 100 g/Nm.sup.3 given in the item of the
cleaning portion A) (labeled as the "O.sub.3 process" in Table 3) is
employed. For the sake of comparison, both the substrate on which the film
is formed after executing the cleaning process by using the N.sub.2 (the
heating temperature is set identically to that in the O.sub.3 process)
under the same conditions as above (labeled as the "N.sub.2 process" in
Table 3) and the substrate on which the film is formed after executing no
pre-process under the same conditions as above (labeled as the
"unprocessed" in Table 3) are also employed as the examination samples. In
both the O.sub.3 process and the N.sub.2 process, the process time is
changed into three types of 30, 60, 90 sec.
According to the results shown in Table 3, it has been confirmed that, in
the case of the N.sub.2 process which does not contain O.sub.3, the
occurrence of the circular defect can be kept constant regardless of the
process time and thus the number of the circular defect can be halved
rather than the unprocessed case, and as a result a certain effect can be
achieved. On the contrary, in the cases of the O.sub.3 process, the number
of the circular defect is reduced as the progress of the process time, the
number is reduced to 1/10 the unprocessed case at the process time of 90
sec and also reduced to about 1/5 the N.sub.2 process case. It has been
found that the O.sub.3 process is most effective.
In addition, a distinctive feature residing in the case of the O.sub.3
process is that the diameter of the circular defect can be reduced
remarkably. That is, it has been found that, in the unprocessed case, the
average diameter of the circular defect is about 5 mm. In contrast, it has
been found that, if the O.sub.3 process is carried out for 90 sec, the
average diameter of the circular defect is reduced to less than 1 mm, and
also the number of the circular delect whose diameter exceeds 5 mm merely
occupies 11% of the total defect number.
From the above, it may be supposed that the chlorate film which is melted
and then spread is decomposed due to the dissociation under the presence
of O.sub.3 and then escaped from the surface of the substrate. In this
case, if it can be assumed that mainly the chlorine is escaped, the
remaining potassium oxide is not thermally stable and thus is escaped
easily from the film-forming surface since the potassium oxide has the
decomposition point of 350.degree. C. and such decomposition point is
lower than the film forming temperature (400.degree. C. to 500.degree.
C.).
Accordingly, it is possible to say that the surface cleaning method
according to the embodiment of the present invention is extremely
effective for preventing the disturbance in film formation of the High
O.sub.3 /TEOS-CVDSiO.sub.2 film depending upon the surface contamination
of the alkali salt.
With the above, the present invention has been explained in detail along
the embodiment, but the scope of the present invention is not limited to
the above embodiment being particularly discussed. Variations of the above
embodiment are contained in the scope of the present invention without
departing the gist of the present invention.
For instance, although both the ion irradiation process and the ozone
process have been performed as the pre-process for the substrate surface
in the above embodiment, at least the ozone process should be performed,
as shown in FIG. 3B.
In addition, the gas mixture consisting of the oxygen containing ozone and
the nitrogen has been employed as the ozone containing gas 15. But the
ozone containing gas 15 is not limited to such gas mixture, and other
ozone containing gases may be employed.
Otherwise, the ozone not-containing but oxygen containing gas, as the case
may be employed as the pre-process gas. In this case, reactivity in the
oxidation reaction may be enhanced by the substrate heating or the
plasmanization of the pre-process gas.
Although preferably the substrate heating temperature in the pre-process is
set to more than 400.degree. C., it is not limited to such temperature and
the substrate heating temperature in the pre-process may be selected
arbitrarily according to material of the particles. In other words, any
substrate heating temperature may be selected if it exceeds the
decomposition point of the particle oxide 13a.
In addition, although the present invention is applied to the case where
the surface 12 of the substrate 11 is formed of the silicon surface, the
present invention is not limited to such case. The present invention may
be applied to the case where the insulating film such as the oxide film,
the nitride film, etc. is exposed on the surface 12, the case where the
conductive film such as the wiring, etc. is exposed, or the case where
both the insulating film and the conductive film are exposed.
In addition, although the gas mixture of the gas containing the ozone in
the oxygen and the gas containing TEOS is employed as the film forming
gas, such film forming gas is not limited to this. A gas mixture of
consisting of the gas containing the ozone in the oxygen and
trimethoxysilane (TMS: (CH.sub.3 O).sub.3 SiH), hexamethyldisilazane
(HMDS), hexamethyldisiloxane (HMDSO), or the like may be employed as the
film forming gas.
Further, although the present invention is applied to the case where the
particles 13 are formed of the alkaline metal salt, the present invention
is not limited to such case. The present invention may be applied to the
case where the particles 13 before the pre-process are formed of alkaline
earth metal salt, e.g., alkaline earth metal chloride (MgCl.sub.2,
CaCl.sub.2, etc.). For example, CaCl.sub.2 has the high decomposition
point (in this case, which is equivalent to about 1935.degree. C. as the
boiling point) and is stable, but it produces unstable calcium chlorate
(Ca(ClO.sub.3).sub.2) when oxidized by the pre-process. Thus, the
decomposition point of (Ca(ClO.sub.3).sub.2) is lowered to about
340.degree. C. which is equivalent to the melting point.
Further, the ozone concentration in the pre-process gas is set to 100
g/Nm.sup.3 in the above embodiment, but the present invention is not
limited to such value. It is preferable that such ozone concentration
should be set to more than 10 g/Nm.sup.3, if possible, in order to have a
sufficient oxidizing force.
Furthermore, the present invention is applied to the pre-process for the
substrate surface prior to the formation of the insulating film, but the
present invention is not limited to such pre-process. The present
invention may be applied to the pre-process for the substrate surface
prior to the formation of the conductive film, the pre-process for
ion-implantation, and the preprocess for the substrate surface before
other steps are carried out.
As described above, according to the present invention, when the particles
are stuck onto the surface of the substrate, the oxidized particle is
generated by exposing the surface to the ozone containing gas end is then
heated at the temperature in excess of the decomposition point of the
particle oxide. Therefore, the particles can be effectively removed and
also the surface, of the substrate can be cleaned.
Moreover, if the film is formed on the cleaned surface of the substrate by
the chemical vapor deposition using the film forming gas like the gas
mixture consisting of the ozone containing gas and the silicon containing
gas, which is affected strongly by the surface dependency, such surface
dependency in forming the film can be eliminated and thus the silicon
containing insulating film can be formed normally.
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